Sex organ

Flowers are the sex organs of flowering plants.

A sex organ or primary sexual characteristic, as narrowly defined, is any anatomical part of the body involved in sexual reproduction and constituting the reproductive system in a complex organism, especially the external sex organs; the external sex organs are also commonly referred to as the genitalia or genitals.^[1][2]

Flowers are the reproductive organs of flowering plants,^[3] cones are the reproductive organs of coniferous plants,^[4] whereas mosses, ferns, and other similar plants have gametangia for reproductive organs.^[5]

Terminology

The Latin term genitalia, sometimes anglicized as genitals, is used to describe the externally visible sex organs, known as primary genitalia or external genitalia: in male mammals, the penis and scrotum; and in female mammals, the clitoris and vulva.

The other, hidden sex organs are referred to as the secondary genitalia or internal genitalia. The most important of these are the gonads, a pair of sex organs, specifically the testes in the male or the ovaries in the female. Gonads are the true sex organs, generating reproductive gametes containing inheritable DNA. They also produce most of the primary hormones that affect sexual development, and regulate other sexual organs and sexually differentiated behaviors.

A more ambiguously defined term is erogenous zone, subjectively, any portion of the body that when stimulated produces erotic sensation, but always prominently including the genitalia.

In general zoology, given the great variety in organs, physiologies, and behaviors involved in copulation, male genitalia are more strictly defined as "all male structures that are inserted in the female or that hold her near her gonopore during sperm transfer"; female genitalia are defined as "those parts of the female reproductive tract that make direct contact with male genitalia or male products (sperm, spermatophores) during or immediately after copulation".^[6]

Mammals

External and internal organs

The visible portion of the mammalian genitals for males consists of the scrotum and penis; for females, it consists of the labia, clitoris, and vagina.

In placental mammals, females have two genital orifices, the vagina and urethra, while males have only one, the urethra.^[7] Male and female genitals have many nerve endings, resulting in pleasurable and highly sensitive touch.^[8][9] In most human societies, particularly in conservative ones, genitals are considered a public indecency and sometimes even illegal if left uncovered in public.^[10]

In mammals, sex organs include:

Female	Male
Bartholin's glands Cervix Clitoris Clitoral frenulum Clitoral glans (glans clitoridis) Clitoral hood Fallopian tubes Labia Labia majora Labia minora Frenulum of labia minora Ovaries Skene's gland Uterus Vagina Vulva An image of human female external sex organs (shaved pubic hair)	Bulbourethral glands Epididymis Penis Foreskin Frenulum of penis Glans penis Prostate Scrotum Seminal vesicles Testicles An image of human male external sex organs

Development

In typical prenatal development, sexual organs originate from a common anlage anatomy during early gestation and differentiate into male or female variations. The SRY gene, usually located on the Y chromosome and encoding the testis determining factor, determines the direction of this differentiation. The absence of it allows the gonads to continue to develop into ovaries.

Thereafter, the development of the internal reproductive organs and the external genitalia is determined by hormones produced by certain fetal gonads (ovaries or testes) and the cells' response to them. The initial appearance of the fetal genitalia (a few weeks after conception) looks basically feminine: a pair of "urogenital folds" with a small protuberance in the middle, and the urethra behind the protuberance. If the fetus has testes, and if the testes produce testosterone, and if the cells of the genitals respond to the testosterone, the outer urogenital folds swell and fuse in the midline to produce the scrotum; the protuberance grows larger and straighter to form the penis; the inner urogenital swellings grow, wrap around the penis, and fuse in the midline to form the penile urethra.

Each sexual organ in one sex has a homologous counterpart in the other one. See a list of homologues of the human reproductive system. In a larger perspective, the whole process of sexual differentiation also includes development of secondary sexual characteristics such as patterns of pubic and facial hair and female breasts that emerge at puberty. Furthermore, differences in brain structure arise, affecting, but not absolutely determining, behavior.

Intersex is the development of genitalia somewhere between typical male and female genitalia. Once the child is born, the parents are faced with decisions that are often difficult to make, such as whether or not to modify the genitalia, assign the child as male or female, or leave the genitalia as is. Some parents allow their doctors to choose. If they do decide to modify the genitalia, they have approximately a 50% chance of getting genitalia that will match the child's gender identity. If they pick the wrong one, their child may begin to show symptoms of transsexualism, which can lead them to a life of discomfort until they are able to remedy the issue.^[11]

Because of the strong sexual selection affecting the structure and function of genitalia, they form an organ system that evolves faster that any other.^[12] A great variety of genital form and function may therefore be found among animals.

Plants

Flowering plants

Sexual reproduction in flowering plants involves the union of the male and female germ cells. The sex organs, contained within the flower, may contain both male and female sex organs (these are known as perfect, bisexual, or hermaphrodite) or only one of the two (known as imperfect or unisexual). Also, those plants whose flowers are unisexual may contain both male and female flowers, or there may be purely male and female plants of the same species.

During a plant's sexual reproduction the stamen (male sex organ) produces pollen from an anther. These male germ cells are carried to the pistil (female sex organ), with the ovary at its base where fertilization can take place. The male germ cells can be carried by air, rain, water, insects, or other symbiotic animals, or simply by gravity.

See also

References

Further reading

Wikimedia Commons has media related to Sexual anatomy.

• Leonard, Janet L. and Alex Córdoba-Aguilar (2010). The Evolution of Primary Sexual Characters in Animals. Oxford: Oxford University Press. ISBN 0199717036.